Turbochargers for gasoline and diesel internal combustion engines are known devices used in the art for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft. Thus rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted to a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
Turbines generally comprise a turbine wheel mounted in a turbine chamber, an inlet passage extending radially inwards towards the turbine chamber, an inlet chamber arranged around the radially outer end of the inlet passage, and an outlet passage extending axially from the turbine chamber. The passages and chamber communicate such that pressurized gas admitted to the inlet chamber flows through the inlet passage to the outlet passage via the turbine chamber, thereby driving the turbine wheel. In the case of a turbocharger for an internal combustion engine, the turbine wheel drives a shaft, which in turn drives a rotary compressor.
There are currently various known turbocharger designs, relating mainly to various arrangements of the vanes in the turbine. In the turbochargers that are hitherto available in the market, it is often desirable to control the flow of motive gas to the turbine to improve its efficiency or operational range. In order to accomplish this, the nozzle passages leading to the turbine wheel may be of variable geometry. These variable geometry nozzle passages can be provided by means of a plurality of vanes, which are pivotable so as to alter the configuration of the passages there between. The design of the suspension system used in association with the pivoting vane design is critical to prevent binding of either the suspension system or the vanes.
Variable geometry nozzle inlets are thus employed in turbochargers to increase performance and aerodynamic efficiency. The variable geometry systems may be of the rotating vane type described in U.S. Pat. No. 5,947,681 in which a plurality of individual vanes are placed in the turbine inlet nozzle and their rotation sets the nozzle area and thus the flow volume.
Alternatively the variable geometry may be of the piston or sliding vane type described in U.S. Pat. No. 5,214,920 and U.S. Pat. No. 5,231,831 and U.S. Pat. No. 5,441,383. In these systems vanes are mounted on a cylindrical piston, or to an opposing nozzle wall, and the piston moves concentric with turbine wheel axis of rotation so that the vanes progressively close the gap between the piston and the wall and reduce the area of the nozzle inlet. Variable geometry devices are advantageous in that they are potentially fully modulating, being infinitely adjustable throughout their operating ranges. Full flow passes through the turbine at all times (except during engine braking) and so the engine backpressure is greatly reduced.
An example of such a VGT a disclosed in U.S. Pat. No. 6,269,642, as one comprising a moveable unison ring disposed within a turbocharger housing of the turbocharger, and a plurality of vanes rotatable disposed within the housing and coupled to the unison ring. The plurality of vanes is interposed within the turbine housing between an exhaust gas inlet and a turbine wheel. The unison ring is operated to rotate the vanes in unison from a closed position (restricting passage of exhaust gas to the turbine wheel) to an open position (enabling passage of exhaust gas to the turbine wheel) for purpose of controlling the turbocharger to perform in a manner that helps to optimize airflow to the engine.
Patent No. WO/2004/022924 discloses a turbine housing having an inlet passage for receiving exhaust gas from an exhaust manifold of an internal combustion engine, the turbine housing also having an exhaust outlet, a turbine wheel carried within the turbine housing, the turbine wheel being connected to a shaft extending from the turbine housing through a shaft bore via a bearing, to a compressor impeller; a piston, arranged concentric to the turbine wheel and movable parallel to the shaft of the turbine wheel; a plurality of vanes extending substantially parallel to the shaft from a first end of the piston across the inlet passage variably to restrict the flow of exhaust gas to the turbine wheel; a resilient bias urging the piston towards a position in which the vanes provide maximum restriction to receive exhaust gas in the inlet passage. The resilient bias comprises a spring located within the turbine housing. The spring preload and spring rate are selected to set the passage width, ie the nozzle throat between the turbine housing and the turbine wheel, to the optimum for the prevailing conditions, such as engine flow.
Patent No. EP0226444 discloses a turbocharger system with a suspension for the pivoting vane actuation mechanism of a variable nozzle mechanism for a turbocharger includes rotatable guide vanes mounted on a vane ring within an annular nozzle passageway immediately upstream of the turbine wheel. A unison ring is mounted to rotate to cause pivoting of the vanes, on a mounting, which maintains concentricity between the vane ring and the unison ring. In a preferred arrangement, the vane ring is aligned with the turbocharger housing via dowels extending between the two. These dowels also serve to carry rollers thereon. The rollers provide a surface on which the periphery of the unison ring rides. The invention tends to eliminate binding of the variable nozzle system, and maintains the unison ring and vane ring concentrically aligned during operation. The vane ring is continuously aligned with the turbine sidewall to provide an annular passage with a constant width.
Patent No. WO/2004/022926 discloses a turbocharger which the variable nozzle device of the turbocharger comprises an annular arrangement of vanes between a vane ring and an outer ring, wherein the outer ring is integrally formed with a peripheral ring fitted on the vane ring and fixedly mounted to the center housing. The vanes are pivotally supported on the vane ring and the peripheral ring against an annular disc member supported on the center housing axially urges the vane ring.
Patent No. WO/2005/040560 discloses a turbocharger that includes a vane assembly for guiding flow from the chamber into the turbine wheel, the vane assembly comprising vanes that include at least dividing vanes, the dividing vanes corresponding in number to the number of dividing walls, each dividing vane forming an extension of one of the dividing walls and extending generally radially inwardly from the dividing wall and terminating at a trailing edge of the dividing vane, the dividing vanes thereby extending the sector-division of the turbine housing to the trailing edges of the dividing vanes; and a variable-geometry mechanism comprising a tubular piston disposed radially inward of the chamber, the piston being axially slidable relative to the chamber between a relatively open position and a relatively closed position in which a fractional portion of the axial length of the sectors is blocked by the piston so as to limit flow into the turbine wheel, wherein the piston and the dividing vanes overlap radially, the dividing vanes are mounted on one of the piston and a fixed structure of the turbine, and the dividing vanes are received in axially extending slots of the other of the piston and the fixed structure when the piston is in the closed position.
Patent No. WO/2003/074850 discloses a vane for use in a variable geometry turbocharger, the vane comprising: an inner airfoil surface; an outer airfoil surface oriented opposite the inner airfoil surface, the inner and outer airfoil surfaces defining a vane airfoil thickness; a leading edge positioned along a first inner and outer airfoil surface junction; and a trailing edge positioned along a second inner and outer airfoil surface junction; wherein the vane has an airfoil thickness that is greater than about 0.16 times a length of the vane as measured between the vane leading and trailing edges; and wherein the inner airfoil surface comprises a convex surface portion and a concave surface portion moving from the vane leading edge to the vane trailing edge.
To achieve exhaust gas flow control in such variable nozzle turbochargers multiple pivoting vanes that are positioned annularly around the turbine inlet are used. The pivoting vanes are commonly controlled to alter the throat area of the passages between the vanes, thereby functioning to control the exhaust gas flow into the turbine. In order to ensure the proper and reliable operation of such variable nozzle turbochargers, it is important that the individual vanes be configured and assembled within the turbine housing to move or pivot freely in response to a desired exhaust gas flow control actuation. Vanes used in such known Variable Geometric Turbochargers (VGTs) are not characterized as having an aerodynamic vane, with the vane outer surface and a vane inner surface. Generally speaking a conventional vane has an airfoil thickness that is less than about 0.14, and can be in the range of from about 0.05 to 0.14 the length of the vane (as measured between vane leading and trailing edges). While such conventional slim or thin airfoil vanes are useful for providing peak aerodynamic efficiency in a Variable Geometric Turbocharger (VGT), this particular vane design limits the flow and turbine efficiency throughout the range of motion for the vanes within the turbocharger.
In order to ensure the proper and reliable operation of such Variable Geometric Turbochargers (VGT), it is important that the individual vanes be configured and assembled within the turbine housing to move or pivot freely in response to a desired exhaust gas flow control actuation. Because these pivoting vanes are subjected to millions of high temperature cycles during turbocharger operation it is necessary that any such pivoting mechanism be one that is capable of repeatedly functioning under such cycled temperature conditions without enduring any cycled temperature related material or mechanical problem or failure.
In variable geometry turbochargers of the prior art, attempts have been made to maximize aerodynamic performance, of the vanes, which are subject to extreme temperature variation and mechanical stress. One approach taken to achieve exhaust gas flow control in such Variable Geometric Turbochargers (VGT) involves the use of multiple pivoting vanes that are positioned annularly around the turbine inlet. The pivoting vanes are commonly controlled to alter the throat area of the passages between the vanes, thereby functioning to control the exhaust gas flow into the turbine.
Known multiple vane Variable Geometric Turbochargers (VGT) include vanes that are each configured having a stem projecting outwardly there from, each such stem being positioned within a respective stem opening in a turbine housing or nozzle wall. While the vanes are commonly actuated to pivot vis-ã-vis their stem within the respective openings, it has been discovered that such vane attachment and pivoting mechanism is not without its problems.
Firstly, in order to ensure freely pivoting movement of the vane stem with the opening it is essential that the stem project perfectly perpendicularly from the vane, to thereby avoid undesired binding or otherwise impairment of the vane pivoting movement. Secondary straightening or machining operations are sometimes necessary to ensure the perpendicularity of the vane shafts, which secondary operations can be both time consuming and costly.
Secondly, this type of vane attachment and pivoting mechanism can produce a high cantilevered load on the vane stem when actuated that can also impair free vane pivoting movement, and that can ultimately result in a vane material or mechanical failure.
It is, therefore, desirable that a vane pivoting mechanism be constructed, for use with a variable nozzle turbocharger, in a manner that provides improved vane operational reliability when compared to conventional vane pivoting mechanisms. It is also desired that an improved vane configuration be constructed that provides a throat area that is similar or better than that of the conventional slim airfoil vane configuration, while at the same time provide a throat area turndown ratio that is improved, and an improved turbine efficiency throughout the range of vane movement, when compared to the conventional slim airfoil vane configuration.
There exists a need for a turbocharger capable of overcoming these technical aspects to maximize output pressure and enhance overall performance.
Unlike these conventional Variable Geometric Turbochargers (VGT) turbocharger systems a turbocharger in accordance with this invention has the advantage over the prior art in that it possesses inventive features detailed above and claimed at a later stage.